For a long time there has been a need to be able to accurately hone external surfaces of cylindrical members in a manner that produces an extremely accurate surface of a predetermined size or diameter and preferably to do so by a single stroking operation of the honing member rotating relative to the workpiece. Devices for accomplishing the same have been achieved by internal honing devices including the internal honing device disclosed in Althen U.S. Pat. No. 4,253,279. The Althen patent is assigned to Applicant's Assignee and involves some similar techniques for achieving extremely precise honing operations but on internal bore surfaces rather than on external cylindrical surfaces.
In the past, external finishing of a workpiece has been previously accomplished by grinding or turning, or by using an external lapping hand tool. More recently, Marvin et al U.S. Pat. No. 5,564,972 discloses an outside diameter finishing tool for low tolerance finishing of the outer surfaces of generally cylindrical workpieces such as piston rods. The Marvin et al apparatus includes an outer metallic shell, an inner abrasive layer, and an epoxy or resin layer therebetween, the inner abrasive layer being located on the inner surface of the epoxy or resin layer. The method of forming the Marvin et al tool includes electro-forming the abrasive layer around the outer surface of a rod member which includes a central cylindrical portion as well as an outwardly tapered portion. After the abrasive layer is formed on the outer surface of the rod, the rod is inserted within the metallic shell such that an annular space is maintained between the inner surface of the metallic shell and the abrasive layer formed on the outer surface of the rod. The space is then filled with an epoxy or resin material and, upon curing, the epoxy or resin layer secures the abrasive coated rod within the metallic shell forming a composite structure consisting of the metallic shell, the epoxy or resin layer, the abrasive layer and the rod. The rod is then removed by immersing the composite structure into a caustic solution which dissolves the rod, or by removing the rod by grinding it away. Removal of the rod results in the abrasive layer being attached to the metallic shell solely by the epoxy or resin layer.
One of the main advantages of the present construction over known prior art constructions including the device disclosed in Marvin et al U.S. Pat. No. 5,564,972 is the fact that in the present construction the abrasive layer which is preferably a superabrasive layer is attached to the inner surface of a metal member preferably by means of a metal plating process. This means that with the present construction, there is better support for the abrasive member. This is important when using superabrasives because it means the tool can be used to hone many more surfaces without replacement and can be adjusted, within limits, to maintain a certain diameter for the parts being honed and at the same time compensate for wear of the abrasive layer. The present construction also is advantageous in that the thickness of the layer of the abrasive material can be varied in a relatively easy manner as it is applied to the inner surface of the honing member. This is important in many applications because the first portion of the honing surface preferably has a steeper taper than the other portions and there may be more than one tapered portion at the entrance end of the honing member. In such a construction, most of the abrading will take place in the first portion that engages the work surface and a lesser amount of abrading and also a polishing effect will be produced by the lesser tapered and/or cylindrical portions of the honing member.
In the Marvin et al device, "a substrate material 20, preferably epoxy, secures the inner surface of the abrasive layer 22 within the shell 16". See column 4, lines 16-18. As a result, the Marvin et al abrasive layer, which also may be a superabrasive layer, is located on a layer of epoxy or resin which, by its very nature, is relatively more subject to changes and does not provide the same heat dissipating and support characteristics for the abrasive layer that is provided when the abrasive layer is plated directly onto a metal member such as a member constructed of nickel, iron, copper, chrome and/or various other alloys. The present external honing tool construction therefore provides a more durable and longer lasting tool which includes improved means for both supporting the abrasive layer on the inner surface of the tool as well as dissipating the heat generated during a honing process, all of which increase the accuracy and consistency of honing cylindrical workpiece surfaces to very small tolerances.